The invention concerns a device for transferring a paper web from the press section to the drying section of a paper machine.
Most modern paper machines use rope carriers for "threading" the paper web into the drying section in restarting the paper machine such as after a standstill or web break. These rope carriers are designed as set out below. In each drying cylinder group, two ropes run along the path of the paper web. To begin the threading operation, one introduces a narrow edge strip of the paper web, the so-called transfer strip, into the rope carriers in the drying cylinder group. During this threading phase, the remaining part of the paper web is passed from the screen or from one of the press rolls to a scrap collection container. Next, the transfer strip is widened until it reaches the full width of the web so that, lastly, the entire paper web is passing through the drying section.
As commonly known, the rope carrier is located on the tending aisle edge of the drying cylinders, and at that, outside the paper web width. Therefore, the transfer strip must be diverted sideways from its normal path, before the point of entering the rope carrier.
A prior rope carrier of that type is described in German Patent Publication No. 25 38 846(1). There, the paper web proceeds from a granite roll, which together with another press roll forms the last press gap, freely to a first guide roll and thence, as well freely, to a second guide roll. There, the entrance point of the rope carrier is arranged. In the presence of such open paper trains, the sideways diversion of the transfer strip can be accomplished with relative ease, routing it to the entrance point of the rope carrier. But a disadvantage of this arrangement is the danger of longitudinally stretching the still moist paper web in the unsupported trains.
Therefore, roll configurations have recently been given preference which provide an uninterrupted web guidance from the press section to the drying section. Some examples are shown in the following documents: U.S. Pat. No. 3,874,997; German Disclosure No. 27 30 149 (U.S. Pat. No. 4,183,248); U.S. Pat. Nos. 4,359,827; and 4,359,828.
In all of these prior paper machines, a backing belt of machine width runs over a guide roll arranged in the press section and then to the drying section so as to run over at least its first drying cylinder. Thus, the backing belt carries the paper web from the press section to the drying section in a fashion so as to support it on its way from the press section to the drying sections and so as to not subject it to any appreciable longitudinal stretching.
But difficulties are encountered when such prior paper machines are to be equipped with a rope carrier. (The cited publications do not describe rope carriers or similar devices for threading the paper web into the drying section.) The reason for these difficulties is that with a continuous paper support from the press section to the drying section, the transfer strip will cling to the backing so as to resist sideways deflection or permit sideways deflection only with great difficulty while being guided to the entrance point of the rope carrier.
Therefore, it has also been suggested previously to arrange on a paper machine with continuous paper transfer the entrance point of the rope carrier so as not to be on the first, but be on the second drying cylinder. This type of arrangement has been suggested since the transfer strip leader separates from the backing without any particular measures after passing the first drying cylinder. This occurrence facilitates diverting the transfer strip to the entrance point of the rope carrier. However, in such an arrangement, it may prove to be a hindrance that the entrance point of the rope carrier is then located within the steam cover of the drying section.
As can be appreciated, there has existed a problem in designing a paper machine with continuous paper transfer from the press section to the drying section, and which features a rope carrier, that the threading of the transfer strip to the entrance point of the rope carrier can be accomplished easily and without risk. It would thus be desirable to provide a paper machine with continuous paper transfer from the press section to the drying section, and which features a rope carrier, wherein the threading of the transfer strip to the entrance point of the rope carrier can be accomplished easily and without risk.